This invention relates to a vacuum toilet system.
Vacuum toilet systems have been known for many years. The modern vacuum toilet system comprises a waste-receiving toilet bowl, a sewer pipe that can be placed under a pressure that is substantially lower than that in the interior of the toilet bowl, and a discharge valve for controlling passage of material from the toilet bowl into the sewer pipe. A rinse liquid outlet is provided near the rim of the toilet bowl and is connected through a rinse liquid valve to a source of pressurized rinse liquid. In order to flush the contents of the bowl into the sewer pipe, the discharge valve is opened and the force due to the pressure difference between the interior of the bowl and the sewer pipe imparts a high initial acceleration to the bowl contents. During a flush cycle, the rinse liquid valve is opened and rinse liquid is introduced into the toilet bowl. The rinse liquid aids in cleansing the toilet bowl but does not itself serve to propel the waste from the toilet bowl and along the sewer. Accordingly, a modern vacuum toilet system is able to operate satisfactorily using only a very small quantity of water as rinse liquid, and therefore the vacuum toilet system is normally used in circumstances where water must be conserved. The desired high acceleration necessitates that the sewer pipe be essentially empty, since if the pipe were filled with water it would then be necessary to accelerate a large mass in order to empty the toilet bowl. During a flush cycle, the volume of air that enters the sewer pipe is typically at least 50 times the volume of sewage (waste plus rinse liquid).
Non-recirculating vacuum toilet systems using plain water as a rinse liquid are attractive for use in aircraft. In such a system, it is conventional for the rinse liquid to be provided from the aircraft's potable water system. The potable water system includes a tank, pipes connecting the tank to consuming devices, such as the vacuum toilets and hand basins, and a pump for maintaining the water in the pipes under pressure.
An aircraft toilet system comprises a holding tank for receiving waste material from the toilet bowl. In order to avoid transporting material that could be discharged from the aircraft in flight, gray water, i.e., water that, though not potable, can be discharged into the environment without treatment, e.g. water from hand basins and from galley sinks, is not fed into the vacuum toilet system so that it enters the holding tank but is discharged from the aircraft through a drain mast.
U.S. Pat. No. 4,713,847 issued Dec. 22, 1987, the disclosure of which is hereby incorporated by reference herein, discloses a vacuum toilet system in which a pump is used to deliver rinse water to a toilet bowl under control of a valve that is opened in response to actuation of a flush switch.
It has been proposed that an aircraft vacuum toilet system should employ gray water as the rinse liquid for the vacuum toilets. According to this proposal, which, as far as the applicants are aware, had not been reduced to practice at the time of filing of the co-pending application, a reservoir for collecting gray water would be provided, and each toilet would be provided with means for drawing gray water from the reservoir and delivering it to the toilet in response to actuation of a flush switch.